API: Fix Identity projection for mismatched transform types (#15502)

api/src/main/java/org/apache/iceberg/transforms/Identity.java

@@ -21,6 +21,7 @@
 import java.io.ObjectStreamException;
 import java.util.Set;
 import org.apache.iceberg.expressions.BoundPredicate;
+import org.apache.iceberg.expressions.BoundReference;
 import org.apache.iceberg.expressions.Expressions;
 import org.apache.iceberg.expressions.UnboundPredicate;
 import org.apache.iceberg.relocated.com.google.common.base.Preconditions;
@@ -146,6 +147,10 @@ public UnboundPredicate<T> project(String name, BoundPredicate<T> predicate) {
 
   @Override
   public UnboundPredicate<T> projectStrict(String name, BoundPredicate<T> predicate) {
+    if (!(predicate.term() instanceof BoundReference)) {
+      return null;
+    }
+
     if (predicate.isUnaryPredicate()) {
       return Expressions.predicate(predicate.op(), name);
     } else if (predicate.isLiteralPredicate()) {

api/src/test/java/org/apache/iceberg/transforms/TestProjection.java

@@ -394,4 +394,30 @@ public void testProjectionNames() {
             Projections.inclusive(partitionSpec).project(equal(truncate("string", 10), "abc"));
     assertThat(predicate.ref().name()).isEqualTo("string_trunc");
   }
+
+  @Test
+  public void testIdentityProjectionWithTransformPredicate() {
+    // Regression test for https://github.com/apache/iceberg/issues/15502
+    // Identity-partitioned timestamptz field filtered with hours() should not throw
+    // ValidationException when projecting the predicate.
+    Schema schema =
+        new Schema(
+            required(1, "id", Types.LongType.get()),
+            required(2, "ts", Types.TimestampType.withZone()));
+
+    PartitionSpec spec = PartitionSpec.builderFor(schema).identity("ts").build();
+
+    // hours(ts) = 490674 produces an integer literal that cannot bind to timestamptz.
+    // Without the fix, projectStrict() attempts to create an UnboundPredicate with the
+    // integer literal for a timestamptz field, which fails during binding.
+    Expression hourFilter = equal(hour("ts"), 490674);
+
+    // Inclusive projection: cannot project → falls back to alwaysTrue
+    Expression projected = Projections.inclusive(spec).project(hourFilter);
+    assertThat(projected).isEqualTo(Expressions.alwaysTrue());
+
+    // Strict projection: cannot project → falls back to alwaysFalse
+    Expression strictProjected = Projections.strict(spec).project(hourFilter);
+    assertThat(strictProjected).isEqualTo(Expressions.alwaysFalse());
+  }
 }